1. Field of the Invention
The present invention relates to a material for organic electroluminescence devices and an organic electroluminescence device (hereinafter sometimes referred to as a “device” or an “organic EL”). More specifically, the present invention relates to a technique to reduce the generation ratio of a short-circuit device in the manufacture and increase the manufacturing yield and also relates to a technique to enhance the storage stability of the device.
2. Description of the Related Art
Studies and developments of an organic electroluminescence device are being aggressively made, because high-luminance light emission can be obtained by low-voltage driving. In general, the organic electroluminescence device is composed of a light emitting layer-containing organic layer and a pair of electrodes sandwiching the layer, where an electron injected from a cathode and a hole injected from an anode are recombined in the light emitting layer and the energy of an exciton produced is utilized for luminescence.
For example, International Publication No. 04/044088 describes providing a material for organic EL devices, where an arylamine compound having a chrysene skeletal structure is utilized in the light emitting layer and long-life blue emission with high color purity and high luminous efficiency is thereby obtained, and providing an organic EL device using the material.
High durability capable of withstanding long-term light emission is required of the organic electroluminescence device, but it is well known that intrusion of moisture into the device generates a dark spot and reduces the durability. This is considered to be caused because the water molecule accelerates the chemical decomposition of a material or accelerates the separation at the organic layer-electrode interface.
In this respect, various measures to prevent reduction in the durability due to invasion of moisture are being taken and, for example, dehydration after wet deposition to reduce the water content ratio in a thin film (see, for example, International Publication No. 01/058221), an encapsulated structure to prevent invasion of moisture (see, for example, JP-A-2007-87620 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2006-294534 and JP-A-2006-278067), and use of an absorbent material, a moisture scavenger or the like (see, for example, JP-A-2006-66366 and JP-A-2006-210095) have been disclosed. Also, a technique of performing a heat treatment in vacuum during deposition to remove water is disclosed (see, for example, JP-A-2003-313654).
Furthermore, it is disclosed that in forming a layer by a wet deposition method, water contained in the composition for an organic electroluminescence device is minimized, whereby water is not allowed to remain in the film after drying and deterioration of the characteristics of a device is suppressed (see, for example, JP-A-2009-102656).
On the other hand, as is well known, fine dust contamination of a device causes electrical short-circuit (short) of the device and reduces the yield in the manufacture. As for the method to prevent short due to fine dust contamination, it has been proposed to provide a flattening layer between an anode layer and an organic layer (see, for example, JP-A-11-224781). However, this method cannot prevent a device from defect generation ascribable to fine dust in an organic layer.
Also, a technique of setting the relative humidity to 0.01 ppm or more at the deposition by a wet deposition method and thereby suppressing electrostatic generation during deposition is disclosed (see, for example, JP-A-2009-146691).
Furthermore, it is disclosed that when the relative humidity in a processing step before vapor deposition is set to 0.01 ppm or more, control to keep the environment constant is facilitated and a device can be stably manufactured (see, for example, JP-A-2008-192433).